Vector network analyzers (VNAs) incorporating high frequency transmission/reflection (T/R) test sets are used to determine the transmission and reflection characteristics of various devices under test (DUTs). The measurement accuracy of a VNA generally improves as the impedances of a source port and a load port of the T/R test set more closely match a predetermined characteristic impedance. Unfortunately, limitations of the electronic hardware used within the T/R test set cause impedance mismatches at the source and load ports that increase measurement uncertainty and degrade measurement accuracy. One measurement error originates during reflection measurements of a multiport DUT. For example, when the output port of a two-port DUT is connected to the load port of the T/R test set, the measured reflection coefficient is a function of both the reflection characteristics of the DUT and the impedance of the load port of the T/R test set. As the mismatch between the load port impedance and the predetermined characteristic impedance increases, the error in the reflection measurement increases. This reflection measurement error is most prominent for DUTs such as cables or filters that have low insertion loss and that don't absorb reflections from the load port of the VNA.
A first known method for reducing reflection measurement errors in a VNA relies on a full two port characterization of the DUT, including both forward and reverse transmission and reflection measurements. Based on this two port characterization, a variety of known vector error correction techniques may be used to mathematically correct for the reflection measurement errors. However, in order to apply the known vector error correction techniques when using a T/R test set, the connection ports of the DUT must be physically reversed relative to the source and load ports to acquire the full two port characterization of the DUT. Reversing the connection ports is time consuming and perturbs the operation of the DUT. A second known method for reducing reflection measurement errors involves connecting a matched load to the output port of the DUT prior to making the reflection measurement. The connection of the matched load is also time consuming and perturbs the operation of the DUT. If reflection measurement errors due to impedance mismatches are not corrected in an effort to reduce measurement time and reduce perturbations to the DUT, the reflection measurement accuracy of the VNA is sacrificed.